The inventive subject matter is applicable to the fields of medical testing, physical rehabilitation, athletics, and fitness training. More specifically, the inventive subject matter is applicable to an interactive exercise system that uses an adaptive actuator to continuously adjust resistance provided to the user of the system to optimize muscle strength.
Musculoskeletal disorders are the leading cause of chronic disability in adults worldwide. Most cases of musculoskeletal disorders are mechanical and are not caused by serious conditions. Numerous highly-respected published reports have shown that muscle weakness is a significant cause of musculoskeletal pain and susceptibility to future injuries. This is especially prevalent with the aging population. Exercise that focuses on muscle strength has shown to be effective in: 1) prevention, 2) recovery, and 3) maintenance of pain and related musculoskeletal disorders.
Numerous products have been developed to increase muscle strength, for rehabilitation, to improve or maintain fitness, and to enhance the performance of athletes. Strength can be defined as the ability of a muscle to generate force. In order to increase muscle strength, a muscle needs to move and contract against an opposing force. Historically, this is done with free weights or weight-based machines that work under the influence of gravity.
Typical weight-based machines use a cable and pulley mechanism that moves a weight stack as the force producing element. These weight stack machines are used throughout the majority of commercial health clubs and physical therapy clinics. Typically, the user inserts an engagement pin that determines the number of weight plates in a stack to be lifted. These machines limit the user to selecting a fixed amount of weight, no greater than can be lifted and lowered by the user at the user's weakest position. Furthermore, the increments between the weight settings are rather large so the adjustability is very limited.
An unwanted effect of using weight as the resistance is, it allows the user to jerk the weight through the weakest section of the range of motion. This decreases the efficiency to strengthen the weakest section in the range of motion which is usually the area that needs the most attention. Weight based equipment is also difficult to stop at any point if a user experiences pain or discomfort. If such equipment is not properly stopped, it can place unnecessary stress on the user's muscles, joints, and tendons and presents a substantial risk of injury if the exercise is continued.
The amount of force that can be exerted by a muscle is highly dependent on the direction of movement and the position throughout the range-of-motion. For example, when lifting a weight it feels heavier in some positions than in other positions. Exercising with resistance that is a significant percentage of an individual's maximum capability produces the greatest increases in strength. Conversely, exercising against a light resistance has relatively little effect on building muscular strength.
It is well known that muscle strength is greater during an “eccentric” contraction (lengthening of the muscle) than during a “concentric” contraction (shortening of the muscle). To increase muscle strength, there is a benefit to providing a greater resistance against a muscle in the eccentric direction. This is commonly known in the exercise industry as “negative” strength training. One method of negative strength training requires an additional person who helps lift the weight in the concentric direction and refrains from assisting in the eccentric direction. This method may provide some value, although is imprecise due to assumptions made by the other person on how much assistance to provide and requires the presence of the other person to perform the exercise.
The capability of an individual's strength throughout an exercise is known in muscle physiology as a strength curve. A strength curve is a mathematical model that represents how much force a muscle can produce at specific joint angles. Strength curves fall into three basic categories: 1) ascending, 2) descending, and 3) bell-shaped. A resistance curve describes how various exercises apply force to a muscle. If it is desired to have the muscle to work harder, the resistance needs to match the muscle's strength curve.
An important factor about strength curves concerns the effects of muscular fatigue. For example, a first repetition may feel lighter to the user at the extended point than the next repetitions may feel even through the movement. The final repetition may be able to be started although unable to be completed.
In an attempt to more closely match the user's strength curve, weight stack machines have been developed that have resistance curves. This is typically done by using a spiral cam with a specific profile rather than a circular pulley. However, these machines have been found to be extremely limiting as they only provide a very generic resistance curve, and do not adjust to fit a wide range of users who have much different individual strength curves. Furthermore, the resistance does not change with the level of muscle fatigue. These machines are also restricted to providing the same weight in both the concentric and eccentric directions.
Various ideas have been proposed to overcome some of the disadvantages of weight stack machines. Most of these utilized other forms of generating resistance. For example, hydraulic, pneumatic, electric, and flywheel system have been developed. Since the user is not actually lifting a weight, there is minimal corresponding moment of inertia to overcome, so there is less potential for injury. These systems can also be less intimidating than traditional machines as there are no weights to clang together. While these systems have provided some benefit by eliminating the need for a bulky weight stack, in most cases the results have been less than desirable.
Hydraulic machines have provided some advantages, although they possess certain disadvantages of their own. In general, hydraulic machines are prone to being slow in changing resistance, and the user can only push so hard or fast due to the inherent qualities of hydraulic cylinders. Another adverse effect is undesirable oscillations at the turn around points of an exercise repetition.
Compressed air machines use pressurized cylinders to provide resistance, and for many years they have been used for muscle strengthening. These pneumatic systems are capable of delivering consistent and controlled resistance. Additionally, a system exists to adjust the resistance by a push of a button rather than needing to change a pin in a weight stack.
Pneumatic machines suffer a major limitation as the resistance typically remains fixed through the range-of-motion. They also have relatively imprecise systems for setting the resistance level and are slower at changing the resistance than hydraulic systems. Furthermore, they have the potential for air leaks and require routine maintenance to assure correct operation.
There are also flywheel mechanisms that generate resistance from the inertia of a rotating mass. The user exercises by accelerating, and decelerating the rotation of a device as a line wraps and unwraps around an axle of a flywheel (like a yo-yo). These machines have minimal adjustability and the peak resistance can only be changed in-between exercise repetitions.
There have been a number of attempts to use an electric motor as part of a muscle strengthening system. One machine has used a motor to turn a pulley that moves a cable or belt mechanism. Another machine uses a motor and a drive system that unwinds and winds a line on a spool assembly. This machine is capable of measuring the amount of user resistance by measuring the tension of the spool line. However, the motor does not actively adjust the resistance against the user. Both of these systems do not maintain resistance levels at the turn around point of the exercise repetition. Furthermore, these machines have had difficulty operating in a smooth fluid movement at low torque. This is particularly undesirable from a rehabilitation standpoint.
Isokinetic machines or dynameters have utilized electric motors for rehabilitation and therapy. Specialized isokinetic testing equipment can be used to measure strength at varying joint angles. Isokinetic machines, however, have limitations as they maintain a constant speed regardless of the amount of user force. With some of these machines where resistance is applied only when movement occurs, there is no resistance at the turnaround point or during the eccentric portions of the exercise. These machines also have a disadvantage as they are not developed for a specific exercise, so the muscle is not isolated and the user can inadvertently use other parts of the body during the exercise.
Although exercise machines as discussed above may be useful for a variety of applications, none of them are capable of providing real-time feedback and actively modifying the resistance during an exercise repetition.
Unlike modern aerobic equipment, such as treadmills and stair climbers, that allows the user to interact with the machine while performing the exercise, this feature is not readily available with existing muscle strengthening machines. Thus, these machines are not psychologically rewarding, as they lack the ability to provide motivation or encouragement to engage the user.
It is desirable to track and record an exercise performance so the progress of the user can be analyzed. Data tracking and recording on muscle strengthening machines are not readily available, other than a few instances with specialized rehabilitation equipment. Furthermore, manually generated records are not convenient and lack the detail that can be generated from a computerized system.
All of the above mentioned exercise and rehabilitation machines suffer from one or more disadvantages. Therefore, there remains a considerable need for an improved exercise and rehabilitation system that provides more efficient and effective muscle strengthening, while avoiding the undesirable characteristics of current equipment. Accordingly, such an exercise system is disclosed herein.